1. Field of the Invention
The present invention is generally directed to removal of blockage of tubular tissue and specifically directed to the dissolution of intravascular thrombi.
2. Description of the Background Art
It is well known that the formation of thrombi (clots) in blood vessels is a serious medical malady. Thrombi are correlated to the formation of plaque buildup in blood vessels and when blockage occurs, it is more a result of the thrombi than of the plaque buildup (which is usually referred to as atherosclerosis when it is involved in arteries).
All thrombi need not be treated interventionally, but in many instances thrombi do, in fact, become life threatening and require removal or at least reduction in size. A thrombus is primarily comprised of red blood cells and fibrin. There are several treatments which could be adapted for the removal of thrombi in vessels which involve intravascular catheters. Most such intravascular catheters have been designed primarily for plaque removal and contain an element that vibrates at ultrasonic frequencies. Representative of such atherectomy catheters are U.S. Pat. Nos. 5,069,664, 4,920,954, 4,898,575, and 4,808,153. Some involve cutting the plaque off of the wall of the vessel using a cutting blade. Some may be adapted to facilitate removal of a thrombus in a vessel. For example, DonMichael, et al., in U.S. Pat. No. 4,870,953, describes an intravascular catheter having a bulbous head at its distal end which vibrates at ultrasonic frequencies. It is suggested that such a tip might be useful for disintegrating a thrombus. DonMichael, et al., also teaches the discharge of a radiographic contrast medium from the catheter tip to enable visualization of the cleared vessel. A second cooling solution may be circulated through the catheter to the tip to prevent overheating of the bulbous tip. All the foregoing intravenous catheters have their shortcomings. None are particularly adapted for removing thrombi.
The use of laser catheters for treatment of thrombi is not uncommon, and significant damage to vessels during this treatment have been reported. The use of drugs for the primary dissolution of these clots is extremely common and is often considered the primary treatment of choice when a thrombus is present. These drugs are referred to as thrombolytic agents (meaning clot dissolution or decomposition). The most common thrombolytic agents (drugs) that are used presently in the treatment of vascular thrombosis are such agents as urokinase, streptokinase, TPA, leech saliva and other such pharmaceutical clot dissolving agents. Significant problems such as hemorrhagic complications, early rethrombosis, prolonged infusion times, costs, significant failure rates, etc., are persistent problems with the use of these pharmaceutical agents. To overcome the aforesaid problems with drugs, an intravascular spraying catheter may be placed in or near a thrombus and the clot periodically sprayed (or pulsed) with a thrombolytic agent which facilitates clot dissolution. Using intermittent spraying of thrombolytic agents may enable the use of less drug over a shorter time period to effect for thrombolysis when compared to the more classical approach of allowing the drug to drip in or near the clot. But even this approach requires excessive time and drug amount. In addition, the use of pulsatile injections of thrombolytic agents may result in pieces of the clot fracturing off from the main body of the clot and causing an embolism which is a danger faced by interventionalists performing this procedure. It is, therefore, desirable to provide an improved catheter for delivering thrombolytic agents which reduce the time and amount of pharmaceutical agent required for thrombolysis and which reduces the danger of embolism.
Stiles, in U.S. Pat. No. 4,692,139 (incorporated herein by reference), describes a catheter for removing obstructions from biological ducts which transmits ultrasonic vibrations to the obstruction to facilitate lysis. Stiles"" catheter has means for administering a lysing agent and simultaneously administering ultrasonic vibrations to obstructing material forward of the catheter tip. The Stiles catheter has a vibrating probe which probe (when the catheter is deployed within a vessel) projects from the tip of the catheter. There is no teaching of any advantages to be gained by either (a) vibrating the catheter (as opposed to a probe housed within a catheter), or (b) using low frequencies (frequencies below 1000 Hz). Further, Stiles teaches the use of vibrational frequencies in the range xe2x80x9cof at least 60 KHz.xe2x80x9d The vibrational frequency employed to effect lysis is an important issue. It is noted that at the frequencies suggested by Stiles"" teaching, the wavelength of ultrasound in the probe is   λ  =            v      f         less than           1000      f         less than           1000              60        ,        000            
or xcex less than 1/60 foot. Thus, in Stiles"" catheter there are normally many wavelengths of ultrasound between the ultrasonic source and the probe tip. Wherever the probe tip touches the surrounding aspiration tube walls and/or aspirate, energy will be lost due to heating. Thus, it is difficult or impossible to control the amount of ultrasonic vibratory energy reaching the tip of the probe. Depending on the amount of loss of ultrasonic vibrational energy that occurs along the length of the probe (which, of course, depends on the amount of aspirate in the aspirator tube and the amount of mechanical contact between the probe and the surrounding walls) the energy actually delivered to tissue at the probe tip may either ablate or weld tissue, emulsify an obstruction or be insufficient to have any effect on an obstruction.
Lower frequency vibrations (less than 100 Hz) have wavelengths greater than one foot. The amplitude and, therefore, the energy of the low frequency vibration delivered to the tip of a catheter is much more predictable at the lower frequencies and enable more accurate dosimetry. This is because the vibratory loss to surrounding tissue is due to uniform frictional losses along the length of the elongate member (inserted catheter). Stiles"" probe, which vibrates at ultrasonic frequencies as noted above, is housed within an aspiration tube where it may unpredictably be loaded by contact with any aspirate that may be present or the surrounding catheter walls. That is, the undesirable coupling of vibratory energy out of the Stiles"" probe is unpredictable. It would be desirable to provide an interventional catheter having a structure wherein the vibrating element contacts the tissue along its entire length.
All of the prior art thrombolysis catheters have specified ultrasonic frequencies (above audible frequencies) when advocating adjunctive vibratory waves to assist thrombolysis. Perhaps this is due to the availability of compact solid state crystals that oscillate or may be driven at these frequencies. Perhaps it is the belief that these frequencies assist in xe2x80x9cemulsifyingxe2x80x9d an obstruction such as a thrombus. Whatever the reason, the present teaching surprisingly shows that the application of low frequency mechanical vibrations facilitate thrombus disintegration. Even more surprisingly, this is true even in the absence of an exogenous lysing agent.
While the invention is best understood and taught by making reference to the invention in context of a particular application such as the treatment of vascular thrombosis, it is the object of the present invention to provide a catheter (herein alternatively referred to as a xe2x80x9cmotion catheterxe2x80x9d or a xe2x80x9cvibrating catheterxe2x80x9d) that can be placed in a blocked lumen in the body and, by either utilizing the motion of the catheter alone or the catheter motion in combination with the dispensing of a medicament suitable for dissolving such blockage, dislodge or more preferably, dissolve said blockage. This motion catheter, which may be simply a moving wire, can be used alone for blockage removal or with a lysing agent to dissolve the blockage. Most preferably, both motion and dispensing are used in combination to effect blockage removal.
The objects of this invention are achieved, in general, by providing a vibrating wire, or alternatively, a vibrating catheter that has an open lumen for delivery of said lysing agents. The vibrating catheter may have one or more directional channels for delivery of a lysing agent which channel(s) are attached to a pump so that delivery of said lysing agent can be controlled with respect to delivery time and delivery rate of the lysing agent.
Because blockage of lumens in the body are often times visualized with image enhancement devices, the catheter of the present invention is conveniently placed by means of fluoroscopy, ultrasound or the like. The motion catheter may be placed in the body in any tubular tissue in proximity to said blockage so that the motion of the catheter will dislodge or preferably dissolve the blockage.
A specific application of the aforementioned motion catheter is the dissolution of blood clots or thrombi with or without the use of a lysing/thrombolytic agent such as urokinase, streptokinase or a similar lysing agent. If the distal tip of the motion catheter is placed in juxtaposition to a blood clot (proximal, distal, inside or adjacent to the clot), the low frequency (1-5000 Hz) motion of the catheter facilitates the dislodgment by mechanical agitation of the thrombolytic clot. Dissolution may be achieved if the vibrating catheter also dispenses a thrombolytic agent. Usually the thrombi are located in an artery. As a thrombus dissolves, it is desirable that the tip of the motion catheter be moved (with regard to its original placement/location) to keep the tip in juxtaposition with the clot and to further facilitate the dissolution of the thrombi.